Cross sections for ionization and excitation in the two-photon transitions of CO B-X(0,0)
High-resolution spectroscopy of CO B-X is being performed to measure cross sections for the processes of two-photon absorption and ionization that underlie two methods often used for sensitive detection of CO in flames, namely, two-photon LIF and 2+1 resonance-enhanced multiphoton ionization (REMPI) via B(v=0). The use of multiphoton excitation is, for even LIF diagnostics, a practical necessity since the allowed one-photon transitions from CO X(v=0) begin at 152 nm. Two 230-nm photons, however, promotes transitions within B{l_arrow}X(0,0); detection in LIF then proceeds by collecting blue to green fluorescence in the Angstrom bands (B{r_arrow}A). In 2+1 REMPI, the ions (or electrons) are monitored as produced by a third ionizing photon at 230 nm that connects B(v=0) to the continuum. The signals acquired with either technique depend on the two-photon excitation rate and also on the ionization rate - a gain in REMPI signal from increased ionization is a loss to LIF in the manner of quenching. The authors have found no direct measurement of the ionization cross section of CO-B in the literature, in that all reported cross sections are extracted from measured trends of REMPI or fluorescence signals versus laser. A rate-equation analysis of a multi-level system was the usual model, with cross sections for intensity, two-photon absorption and ionization varied for best match with the measured trends. Further, only one such study, that of Looney et al., has offered a cross section for the photo-ionization of CO-B at 230 nm.
- Research Organization:
- Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)
- Sponsoring Organization:
- USDOE, Washington, DC (United States)
- DOE Contract Number:
- AC04-94AL85000
- OSTI ID:
- 486019
- Report Number(s):
- SAND-97-8579C; CONF-970495-3; ON: DE97052742; TRN: 97:004002
- Resource Relation:
- Conference: Western State section of the Combustion Institute meeting, Livermore, CA (United States), 14-15 Apr 1997; Other Information: PBD: 1997
- Country of Publication:
- United States
- Language:
- English
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